CN105717156A - Double-probe thermal pulse thermal characteristic measuring system capable of calibrating probe interval in situ and method - Google Patents

Abstract

The invention discloses a double-probe thermal pulse thermal characteristic measuring system capable of calibrating the probe interval in situ by itself and a method based on the system. By means of the system and the method, thermal characteristic parameter measurement errors caused by changes of the probe interval can be reduced. The system comprises a heating probe, a base, a heating device, a data processing device and at least one temperature probe, wherein the base is used for fixing the heating probe and the temperature probes; a heating wire is arranged in the heating probe, the ratio of the length to the inner diameter of the heating probe is larger than a preset numerical value, and the heating probe conducts heating through the heating device; at least three temperature measuring elements are arranged in each temperature probe in the axial direction; the data processing device is connected with temperature measuring elements and used for obtaining temperature response data collected by the temperature measuring elements after the heating probe and the temperature probes are inserted into a substance to be measured, obtaining the actual interval between each temperature measuring element and the heating probe according to the temperature response data and obtaining thermal characteristic parameters of the substance to be measured through fitting according to the actual interval.

Description

Double-needle heat pulse thermal characteristic measuring system and method capable of calibrating probe distance in situ

Technical Field

The invention relates to the technical field of thermal characteristic measurement, in particular to a double-needle thermal pulse thermal characteristic measurement system capable of in-situ self-correcting probe spacing and a measurement method based on the system.

Background

At present, a single-needle heat pulse method and a double-needle heat pulse method are widely used for measuring thermal characteristics of materials such as soil, rocks, food, combustible ice, and the like. The single-needle heat pulse method can only measure the heat conductivity of the substance and cannot simultaneously obtain the specific heat and the thermal diffusivity of the substance to be measured. The two-pin heat pulse method can simultaneously measure the thermal conductivity, the thermal diffusivity and the specific heat, so that the two-pin heat pulse method is more used in the current practical measurement and application.

The measuring device of the double-needle heat pulse method comprises two or more parallel stainless steel probes with a distance r, wherein one probe is provided with a heating wireThe thermal probes, and one or more of the thermal probes, are temperature probes having temperature sensing elements, and the spacing between the thermal probes and the thermal probes is calibrated with a material having known thermal properties. The probe is inserted or put into a substance to be measured, heat emitted by the heating probe after electrification is conducted to the temperature probe through a medium to be measured, and the temperature probe senses and records the change of temperature along with time. At present, the duration t is obtained on the assumption of an infinitely long linear heat source (ILS) which is commonly used₀The thermal pulse signal of (2) induces an analytical solution of the temperature change of the temperature probe at a distance r from the heating needle (deVries, 1952; kluitenberget, 1993):

$\mathrm{\&Delta;}T(r,t)=\left\{\begin{array}{cc}\frac{-q^{\&prime;}}{4\mathrm{\&pi;}\mathrm{\&alpha;}\mathrm{\&rho;}c}Ei\&lsqb;\frac{-r^2}{4\mathrm{\&alpha;}t}\&rsqb;& t<t_0\\ \frac{q^{\&prime;}}{4\mathrm{\&pi;}\mathrm{\&alpha;}\mathrm{\&rho;}c}\{Ei\&lsqb;\frac{-r^2}{4\mathrm{\&alpha;}(t-t_0)}\&rsqb;-Ei\&lsqb;\frac{-r^2}{4\mathrm{\&alpha;}t}\&rsqb;\}& t>t_0\end{array}\right.,---\&lsqb;1\&rsqb;$

wherein, -Ei (-x) is an exponential integration function; q' is the heating intensity; t is t₀And rho is the density, and meets the condition that rho c is lambda/α, and the thermal characteristic parameters of the sample to be measured, such as the thermal conductivity, the specific heat and the like, can be obtained by carrying out nonlinear parameter regression on the equation.

Furthermore, the following single point method can also be used for the calculation of the thermal properties: bristow wet (1994) calculates the partial derivative of the temperature t according to equation [1] and makes the result equal to zero, obtaining the thermal diffusivity, α, and the specific heat, c, as follows:

$\mathrm{\&alpha;}=\frac{r^2}{4}\left\{\frac{1/(t_m-t_0)-1/t_m}{ln\&lsqb;t_m/(t_m-t_0)\&rsqb;}\right\}---\&lsqb;2\&rsqb;$

$c=\frac{q^{\&prime;}}{4{\mathrm{\&pi;\&rho;\&alpha;\&Delta;T}}_m}\{Ei\&lsqb;\frac{-r^2}{4\mathrm{\&alpha;}(t_m-t_0)}\&rsqb;-Ei\left(\frac{-r^2}{4{\mathrm{\&alpha;t}}_m}\right)\}---\&lsqb;3\&rsqb;$

wherein, Delta T_mIs the maximum value of the temperature rise, t_mIs a temperature rise to a maximum value Δ T_mThe thermal conductivity λ can be obtained from the thermal diffusivity α and the specific heat c, that is, λ ρ c · α.

In the above-mentioned two-pin heat pulse method, the probe spacing r is a very important parameter, and the measurement error of r has a great influence on the accuracy of the measurement result of the thermal characteristic. Errors in the probe's included angle at one degree can cause errors in specific heat measurements of over 14% (liuetal., 2008; wenetal., 2015). Campbell et al (1991) showed that a 2% deviation from the probe spacing resulted in a 4% error in measuring the specific heat of the substance to be measured. However, in practical applications, especially in the field, due to the existence of crushed stones, spatial heterogeneity, development of the underground root system of plants, activity of soil protozoa, and the effects of expansion and contraction, freeze-thaw alternation, etc., the probe placed in the material to be tested is easily bent and deformed. After the probes are bent, the distance between the probes can be changed, and the specific heat/thermal diffusivity measurement error of the double-needle method is very sensitive to the distance change, so that the measured specific heat/thermal diffusivity has a large error finally.

In order to eliminate specific heat and thermal diffusivity measurement errors caused by probe bending deformation, the problem of in-situ on-site calibration of probe spacing needs to be solved. The problem puzzles relevant research on geophysical science, soil science and meteorological science for many years. The mainstream treatment to date is negatively conservative: assuming that the probe spacing does not change after placement in the field, or even if the spacing changes due to flexural deformation, the spacing remains unchanged, a calibration given by materials with known thermal properties such as laboratory agar is used.

Recognizing the importance of accurately measuring the pitch in situ, Liu et al (2013) propose a method that can correct linearly curved probe pitch in the field. By axially placing two temperature measuring units in the same temperature probe, exploratory research of in-situ calibration of probe distance is realized. However, this method includes many assumptions, and thus has many limitations in practical applications. First, their research is limited to temperature probes that are bent, and these assumptions do not match reality, provided that the heating probe does not change. In addition, another drawback of this method is also the most important one: their theoretical basis is based on the assumption that the bending deformation of the temperature probe is linear. In fact, it is known from structural mechanics that the bending of a beam under applied stress is nonlinear, as a result of studies of the deformation of the beam under stress (Beer et al, 2006).

In summary, in practical applications, the bending deformation of the probe should be non-linear, rather than the linear deformation assumed by Liu et al (2013). It is less likely that only the temperature probe will bend, the heating probe will remain free of deformation bending at all times, as assumed by Liu et al (2013). Therefore, there is a limit to the improvement of the calibration effect after the pitch calibration method of the in-situ two-pin heat pulse probe using the temperature probe of linear bending deformation of Liu et al (2013). After analyzing the processed data by the method, great errors still exist in specific heat and thermal diffusivity.

However, the research methods and contents of the application and Liu et al (2013) still have significant essential differences. Firstly, the method of Liu et al (2013) is to obtain the bending deformation of the temperature probe by linear approximation according to the basic geometrical principle that a straight line can be determined by two points by introducing two temperature measuring units into the same temperature probe. According to the common knowledge of geometry, at least three points are needed to approximate a curve. Approximating a curve with a straight line will in most cases result in large errors, especially when the curvature of the curve is large.

Based on the above analysis, it can be known that, according to the existing research method, in order to fundamentally eliminate the measurement errors of the dual-needle thermal pulse probe about specific heat and thermal diffusivity, which are more common and caused by nonlinear bending deformation, a new method suitable for in-situ calibration of nonlinear deformation is urgently needed to be developed, and the main content of the research is introduced.

Disclosure of Invention

Technical problem to be solved

The invention aims to provide a system and a method for measuring thermal characteristics of a double-needle thermal pulse, which can be used for in-situ self-correcting the probe distance, and can effectively reduce the measurement error of thermal characteristic parameters caused by the distance change caused by the nonlinear bending deformation of a probe. Compared with the existing method (Liu et al, 2013), the research has remarkable advantages and advantages.

(II) technical scheme

Specifically, the present invention includes the following:

the invention provides a double-needle heat pulse thermal characteristic measuring system capable of in-situ self-correcting probe spacing, which comprises a heating probe, a heating device, a data processing device, a base and at least one temperature probe, wherein the temperature probe and the heating probe are fixed on the base in parallel, a heating wire is arranged in the heating probe, the ratio of the length to the inner diameter of the heating probe is larger than a preset value, the heating probe is connected with the heating device and is used for heating by utilizing the heating device, at least three temperature measuring elements are arranged in each temperature probe along the axial direction of the temperature probe, the data acquisition processing device is connected with the temperature measuring elements and is used for acquiring data of temperature evolution along with time, which are acquired by the temperature measuring elements, after the heating probe and the temperature probe are inserted or placed in a substance to be detected, so as to generate a curve of temperature change along with time, and according to the curve, combining a given in-situ nonlinear bending probe spacing calculation formula to obtain an actual spacing between the temperature measuring element and the heating probe, and according to the actual spacing, calculating the thermal characteristic parameters of the substance to be measured by a single point method or a nonlinear parameter fitting and regression analysis method.

Content 2: the invention provides a double-needle heat pulse thermal characteristic measuring method capable of in-situ self-correcting probe spacing, which comprises the following steps:

s1: calibrating an initial spacing between each temperature sensing element in the temperature probe and the heating probe with a material having known thermal property parameters;

s2: inserting the temperature probe and the heating probe into a substance to be detected, measuring by a data processing device to obtain a curve of temperature changing along with time, calculating the actual distance between each temperature measuring element and the heating probe according to the curve of temperature changing along with time and the initial distance, and calculating the thermal characteristic parameter of the substance to be detected by a single-point method or a nonlinear parameter fitting method according to the actual distance.

(III) advantageous effects

The invention can carry out in-situ self-correction on the probe spacing in comparison with the prior art of linear bending correction, therefore, the invention can reduce the measurement error of the thermal characteristic parameter caused by the change of the probe spacing caused by nonlinear bending deformation, compared with the probe bending, the invention can not carry out in-situ correction or can correct but can reduce the measurement error of the thermal characteristic parameter caused by the change of the probe spacing on the basis of the prior art of linear bending correction, thereby not only improving the accuracy of the two-needle thermal pulse method applied to measuring the thermal characteristic of a substance in the field, and the development of the double-needle heat pulse method is promoted, and in addition, the system has the advantages of simple structure, low manufacturing cost, convenience in use and quickness in measurement.

Drawings

FIG. 1 is a schematic partial structural view of an embodiment of a dual-probe thermal pulse thermal characterization system with in-situ self-calibration of probe spacing according to the present invention;

FIG. 2 is a schematic diagram of the probe of FIG. 1 after tilting inward (taking three temperature sensing elements in each temperature probe as an example);

FIG. 3 is a schematic flow chart of a method for measuring thermal characteristics of a dual-probe thermal pulse capable of in-situ self-calibration of probe spacing according to the present invention;

wherein: 1-a temperature probe; 2-heating the probe; 3-a base; 4-a first temperature measuring element; 5-a second temperature measuring element; 6-third temperature measuring element.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the embodiments of the present invention will be described in detail with reference to the accompanying drawings, and it is to be understood that the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without any creative work belong to the protection scope of the present invention.

As shown in fig. 1, the embodiment discloses a dual-probe thermal pulse thermal characteristic measurement system capable of in-situ self-correcting probe spacing, which includes a heating probe 2, a heating device, a data processing device, a base 3 and at least one temperature probe 1, wherein the temperature probe 1 and the heating probe 2 are fixed on the base 3 in parallel, a heating wire 7 is arranged in the heating probe 2, a ratio of a length to an inner diameter of the heating probe 2 is greater than a preset value, the heating probe 2 is connected to the heating device, the heating device is used for heating, at least three temperature measurement elements (a first temperature measurement element 4, a second temperature measurement element 5 and a third temperature measurement element 6 in fig. 1) are arranged in each temperature probe 1 along an axial direction thereof, the data processing device is connected to the temperature measurement elements and is used for obtaining that the heating probe 2 and the temperature probe 1 are inserted into a substance to be measured, the temperature data that the temperature sensing element gathered (insert the probe or settle in the material that awaits measuring, the heat that sends by heating probe 2 after the circular telegram conducts temperature probe 1 through the medium that awaits measuring, is responded to respectively and is noted the change of temperature along with time by every temperature sensing element in the temperature probe 1), and according to temperature data generate the curve of temperature along with the change of time, obtain according to the curve the actual interval between temperature sensing element and the heating probe 2, calculate according to the actual interval the thermal characteristic parameter (thermal diffusivity, specific heat and thermal conductivity) of the material that awaits measuring.

In the implementation case of the invention, the temperature probe 1 and the heating probe 2 can be both made of stainless steel hollow needle tubes, and the heating wire arranged in the heating probe 2 can be made of nickel-chromium alloy.

The system for measuring the thermal characteristics of the two-pin heat pulse capable of self-correcting the probe spacing in situ, which is disclosed by the embodiment of the invention, can be used for self-correcting the probe spacing in situ, compared with the prior art that the probe is bent and cannot be corrected in situ or can be corrected, but based on the linear bending correction, the system can be used for reducing the measurement error of the thermal characteristic parameters caused by the change of the probe spacing due to the nonlinear bending deformation, so that the accuracy of the two-pin heat pulse method applied to the measurement of the thermal characteristics of the substance in the field is improved, and the development of the double-needle heat pulse method is promoted, and in addition, the system has the advantages of simple structure, low manufacturing cost, convenience in use and quickness in measurement.

Optionally, in the system for measuring thermal characteristics of a two-pin heat pulse capable of in-situ self-correcting probe gap according to the present invention, if there is one temperature probe, the data processing device is configured to obtain a time period during which temperature data acquired by the temperature measuring element rises to a maximum value according to the curve, and calculate an actual gap between the temperature measuring element and the heating probe according to the time period, where a calculation formula is $r_i=a_1{l}_i+a_2{l}_i^2+......+a_{n-1}{l}_i^{n-1}+r_{i0},$

Wherein, a_iBy the formula

$\begin{array}{c}{(r_{10}+a_1{l}_1+\mathrm{......}+a_{n-1}{l}_1^{n-1})}^2{K}_1={(r_{20}+a_1{l}_2+\mathrm{......}+a_{n-1}{l}_2^{n-1})}^2{K}_2=\\ \mathrm{......}={(r_{n0}+a_1{l}_n+\mathrm{......}+a_{n-1}{l}_n^{n-1})}^2{K}_n\end{array}$

The calculation is carried out according to the calculation,r_iis the actual distance between the ith temperature measuring element and the heating probe,/_iIs the distance, r, from the ith temperature measuring element to the base_i0Is the initial spacing, t, between the ith temperature sensing element and the heater probe_miThe time length for the temperature collected by the ith temperature measuring element to rise to the maximum value, i ∈ (1, 2.. multidot.n), n is the number of the temperature measuring elements in the temperature probe, t₀Is the heating time period of the heating probe.

In the embodiment of the invention, the deflection distance of the ith temperature measuring element is expressed by a formula [4]

Δr_i＝Δr_i1+Δr_i2,(i＝1,2……n)[4]

As shown in FIG. 2, ignore Δ r_i1Error between deflection distance of the ith temperature measuring element relative to the initial position by Δ r_i1Indicating the deflection distance of the ith temperature measuring element with respect to the initial position, ignoring Δ r_i2Error between the deflection distance of the heating pin at the same height as the ith temperature measuring element in the heating probe, measured by Δ r_i2The deflection distance of the heating pin at the same height as the ith temperature measuring element in the heating probe is shown in the formula [4]It is meant that our method can be applied to both temperature probe deflection or heater pin deflection, and to both.

To solve for the deflection distance, we assume that the deflection of the probe is a non-linear deflection, expressed as:

${\mathrm{\&Delta;r}}_i=a_1{l}_i+a_2{l}_i^2+\mathrm{......}+a_{n-1}{l}_i^{n-1},(i=1,\mathrm{2......}n)---\&lsqb;5\&rsqb;$

wherein l_iIs the distance from the ith temperature measuring element to the base, a₁,a₂To a_n-1Is n-1 coefficients of an n-1 order polynomial.

r_i＝Δr_i+r_i0，(i＝1,2……n)[6]

Wherein r is_iIs the actual distance, r, from the ith temperature sensing element to the heater probe_i0Is the initial spacing between the ith temperature sensing element and the heater probe.

Then, r can be calculated according to respective temperature-time response curves_iThe detailed calculation steps are given below. Is represented by the formula [2]It is possible to obtain:

${\mathrm{\&alpha;}}_i=\frac{r_i^2}{4t_{mi}}\frac{t_0}{(t_{mi}-t_0)}{\&lsqb;\ln \left(\frac{t_{mi}}{t_{mi}-t_0}\right)\&rsqb;}^{-1}---\&lsqb;7\&rsqb;$

wherein, t_miThe time length for which the temperature collected by the ith temperature measuring element rises to the maximum value is adopted. To simplify the expression, define

$K_i=\frac{1}{t_{mi}}\frac{t_0}{(t_{mi}-t_0)}{\&lsqb;\ln \left(\frac{t_{mi}}{t_{mi}-t_0}\right)\&rsqb;}^{-1}---\&lsqb;8\&rsqb;$

Assuming the measured material is homogeneous, the thermal diffusivity α measured by the n temperature sensing elements in the temperature probe 1₁，α₂To α_iShould be the same. Further according to the formula [6]，[7]And [8 ]]The relationship between the actual spacing of each temperature sensing element from the heating probe can be obtained:

$r_1^2{K}_1=r_2^2{K}_2=\mathrm{......}=r_n^2{K}_n---\&lsqb;9\&rsqb;$

the above expression can also be expressed as:

$\begin{array}{c}{(r_{10}+a_1{l}_1+\mathrm{......}+a_{n-1}{l}_1^{n-1})}^2{K}_1={(r_{20}+a_1{l}_2+\mathrm{......}+a_{n-1}{l}_2^{n-1})}^2{K}_2=\\ \mathrm{......}={(r_{n0}+a_1{l}_n+\mathrm{......}+a_{n-1}{l}_n^{n-1})}^2{K}_n\end{array}$

$\&lsqb;10\&rsqb;$

wherein, K₁,K₂……K_nIs derived from the temperature-time curve, the initial spacing is also known, so that a₁,a₂……a_n-1Can be obtained. Then, combine equation [5]And [6 ]]The actual distance of each temperature measuring element from the heating needle can be determined.

Optionally, in the system for measuring thermal characteristics of a two-pin heat pulse capable of in-situ self-correcting probe gap of the present invention, if there is one temperature probe, three temperature measurement elements are disposed in the temperature probe along the axial direction thereof, the data processing device is configured to obtain, according to the curve, a time length during which temperature data acquired by the temperature measurement elements rises to a maximum value, and calculate, according to the time length, an actual gap between the temperature measurement elements and the heating probe, where a calculation formula is $r_i=\frac{{\mathrm{\&beta;}}_2{\mathrm{\&chi;}}_1-{\mathrm{\&beta;}}_1{\mathrm{\&chi;}}_2}{{\mathrm{\&xi;}}_1{\mathrm{\&beta;}}_2-{\mathrm{\&xi;}}_2{\mathrm{\&beta;}}_1}{l}_i+\frac{{\mathrm{\&xi;}}_2{\mathrm{\&chi;}}_1-{\mathrm{\&xi;}}_1{\mathrm{\&chi;}}_2}{{\mathrm{\&xi;}}_2{\mathrm{\&beta;}}_1-{\mathrm{\&xi;}}_1{\mathrm{\&beta;}}_2}{l}_i^2+r_{i0},$ Wherein, ${\mathrm{\&beta;}}_2=l_2^2-l_3^2{P}_2,$ χ₁＝r₂₀P₁-r₁₀，χ₂＝r₃₀P₂-r₂₀，ξ₁＝l₁-l₂P₁，ξ₂＝l₂-l₃P₂， $P_1=\sqrt{\frac{t_{m1}(t_{m1}-t_0)}{t_{m2}(t_{m2}-t_0)}\ln \left(\frac{t_{m1}}{t_{m1}-t_0}\right){\&lsqb;\ln \left(\frac{t_{m2}}{t_{m2}-t_0}\right)\&rsqb;}^{-1}},$ $P_2=\sqrt{\frac{t_{m2}(t_{m2}-t_0)}{t_{m3}(t_{m3}-t_0)}\ln \left(\frac{t_{m2}}{t_{m2}-t_0}\right){\&lsqb;\ln \left(\frac{t_{m3}}{t_{m3}-t_0}\right)\&rsqb;}^{-1}},$ r_iis the actual distance between the ith temperature measuring element and the heating probe, t_miFor the duration of the temperature rise to the maximum value, l, detected by the ith temperature measuring element_iIs the distance, r, from the ith temperature measuring element to the base_i0Is the initial spacing, i ∈ (1,2,3), t, between the ith temperature sensing element and the heater probe₀Is the heating time period of the heating probe.

In practical applications, three temperature measuring elements are relatively economical and practical choices, so we will specifically describe the solving process by taking three temperature measuring elements as an example.

First, we will refer to the distance of deflection (Δ r) of the three temperature sensing elements_i) Is shown as

${\mathrm{\&Delta;r}}_i={\mathrm{al}}_i+{\mathrm{bl}}_i^2,(i=1,2,3)---\&lsqb;11\&rsqb;$

r_i＝Δr_i+r_i0，(i＝1,2,3)[12]

Where a and b are two coefficients of a second order polynomial, it is of course possible to use a₁,a₂To indicate. When neither a, b is 0, the formula represents a non-linear bend, and when b is 0, the formula becomes a linear bend.

Then, the thermal diffusivity is calculated according to the respective temperature-time response curves, which can be obtained from equation [7 ]:

$\begin{array}{c}{\mathrm{\&alpha;}}_1=\frac{r_1^2}{4t_{m1}}\frac{t_0}{(t_{m1}-t_0)}{\&lsqb;\ln \left(\frac{t_{m1}}{t_{m1}-t_0}\right)\&rsqb;}^{-1}\\ {\mathrm{\&alpha;}}_2=\frac{r_2^2}{4t_{m2}}\frac{t_0}{(t_{m2}-t_0)}{\&lsqb;\ln \left(\frac{t_{m2}}{t_{m2}-t_0}\right)\&rsqb;}^{-1}\\ {\mathrm{\&alpha;}}_3=\frac{r_3^2}{4t_{m3}}\frac{t_0}{(t_{m3}-t_0)}{\&lsqb;\ln \left(\frac{t_{m3}}{t_{m3}-t_0}\right)\&rsqb;}^{-1}\end{array}---\&lsqb;13\&rsqb;$

after that, we define $K_1=\frac{1}{t_{m1}}\frac{t_0}{(t_{m1}-t_0)}{\&lsqb;\ln \left(\frac{t_{m1}}{t_{m1}-t_0}\right)\&rsqb;}^{-1},K_2=$ $\frac{1}{t_{m2}}\frac{t_0}{(t_{m2}-t_0)}{\&lsqb;\ln \left(\frac{t_{m2}}{t_{m2}-t_0}\right)\&rsqb;}^{-1}$ And $K_3=\frac{1}{t_{m3}}\frac{t_0}{(t_{m3}-t_0)}{\&lsqb;\ln \left(\frac{t_{m3}}{t_{m3}-t_0}\right)\&rsqb;}^{-1}.$

assuming that the measured material is homogeneous, the thermal diffusivity α measured by the three temperature sensing elements in the temperature probe 1 is₁，α₂And α₃Should be the same. Further we obtain the relationship between the probe pitches:

$\frac{r_1}{r_2}=\sqrt{\frac{K_2}{K_1}}=P_1---\&lsqb;14\&rsqb;$

$\frac{r_2}{r_3}=\sqrt{\frac{K_3}{K_2}}=P_2---\&lsqb;15\&rsqb;$

P₁and P₂Are parameters introduced to simplify the expression. In addition, according to the formula [14 ]]And [15 ]],P₁And P₂It can also be expressed as:

$\frac{r_{10}+{\mathrm{al}}_1+{\mathrm{bl}}_1^2}{r_{20}+{\mathrm{al}}_2+{\mathrm{bl}}_2^2}=P_1;\frac{r_{20}+{\mathrm{al}}_2+{\mathrm{bl}}_2^2}{r_{30}+{\mathrm{al}}_3+{\mathrm{bl}}_3^2}=P_2---\&lsqb;16\&rsqb;$

to solve a and b, the above formula can be arranged as

$\left\{\begin{array}{c}a(l_1-l_2{P}_1)+b(l_1^2-l_2^2{P}_1)=r_{20}{P}_1-r_{10}\\ a(l_2-l_3{P}_2)+b(l_2^2-l_3^2{P}_2)=r_{30}{P}_2-r_{20}\end{array}\right.---\&lsqb;17\&rsqb;$

Further simplified equation [13]Is prepared by₁-l₂P₁Is defined as ξ₁；Is defined as β₁；r₂₀P₁-r₁₀Is defined as x₁；l₂-l₃P₂Is defined as ξ₂；Is defined as β₂，r₃₀P₂-r₂₀Is defined as x₂. Formula [13]The following steps are changed:

$\left\{\begin{array}{c}{\mathrm{a\&xi;}}_1+{\mathrm{b\&beta;}}_1={\mathrm{\&chi;}}_1\\ {\mathrm{a\&xi;}}_2+{\mathrm{b\&beta;}}_2={\mathrm{\&chi;}}_2\end{array}\right.---\&lsqb;18\&rsqb;$

finally solving the above equation system yields a solution of a and b:

$\left\{\begin{array}{c}a=\frac{{\mathrm{\&beta;}}_2{\mathrm{\&chi;}}_1-{\mathrm{\&beta;}}_1{\mathrm{\&chi;}}_2}{{\mathrm{\&xi;}}_1{\mathrm{\&beta;}}_2-{\mathrm{\&xi;}}_2{\mathrm{\&beta;}}_1}\\ b=\frac{{\mathrm{\&xi;}}_2{\mathrm{\&chi;}}_1-{\mathrm{\&xi;}}_1{\mathrm{\&chi;}}_2}{{\mathrm{\&xi;}}_2{\mathrm{\&beta;}}_1-{\mathrm{\&xi;}}_1{\mathrm{\&beta;}}_2}\end{array}\right.---\&lsqb;19\&rsqb;$

using the values of a and b, according to the equation [11]And [12 ]]Can find out r₁,r₂And r₃。

Alternatively, in another embodiment of the dual-probe thermal pulse thermal property measurement system capable of in-situ self-calibration of probe spacing according to the present invention, the data processing device is configured to calculate the thermal property parameter of the substance to be measured by a single-point method or a nonlinear parameter fitting/regression analysis method according to the actual spacing.

Alternatively, in another embodiment of the dual-probe thermal pulse characteristic measurement system capable of in-situ self-calibration of the probe spacing according to the present invention, the predetermined value is 22.

Optionally, in another embodiment of the dual-pin thermal pulse thermal property measurement system capable of in-situ self-calibration of the probe pitch according to the present invention, the distance between every two adjacent temperature measurement elements is greater than or equal to 2mm, the distance from the temperature measurement element near the top end of the temperature probe to the top end of the temperature probe is greater than or equal to 6mm, and the distance from the temperature measurement element near the base to the base is greater than or equal to 6 mm.

To increase the signal-to-noise ratio, the first temperature sensing element 4 and the second temperature sensing element 5, and the second temperature sensing element 5 and the third temperature sensing element 6, are sufficiently distant from each other in the axial direction of the temperature probe 1. The following describes conditions to be satisfied by the positions of the temperature measuring elements placed in the axial direction of the temperature probe, taking three temperature measuring elements in each temperature probe as an example: the distance between the temperature measuring elements and the top end of the probe and the distance between the temperature measuring elements and the base are both larger than or equal to 6mm, namely, the distance between the first temperature measuring element 4 close to the top end of the temperature probe and the top end of the temperature probe 1 is larger than or equal to 6mm, and the distance between the third temperature measuring element 6 close to the base 3 and the base 3 is larger than or equal to 6 mm. In addition, the distance between two adjacent temperature measuring elements is not less than 2mm, so that the relative deviation between the temperature measured by the temperature measuring elements arranged at the bottom end and the top end of the probe and the temperature measured by the temperature measuring element arranged at the middle position of the probe is less than 1%. The signal-to-noise ratio can be increased and accurate measurement can be guaranteed.

Alternatively, in another embodiment of the dual-pin thermal pulse thermal characterization system of the present invention that is capable of self-calibrating probe spacing in situ, the temperature probe and the heating probe are potted in a curable sealing material on the base.

In the embodiment of the invention, the sealing material can be made of waterproof materials with higher heat conductivity and better electrical insulation so as to ensure that the heating wire and the temperature measuring element are fixed at accurate positions and are insulated from the surrounding environment.

Alternatively, in another embodiment of the dual-pin thermal pulse thermal characterization system of the present invention that is capable of self-calibrating probe spacing, the sealing material is epoxy.

Alternatively, in another embodiment of the dual-pin thermal pulse thermal characterization system of the present invention that is capable of self-calibrating probe spacing, the temperature measuring element is a thermistor or a thermocouple.

In the embodiment of the present invention, the temperature measuring element may be a thermistor or a thermocouple, or may be another suitable temperature measuring element.

As shown in fig. 3, the present embodiment discloses a method for measuring thermal characteristic parameters of a dual-probe thermal pulse thermal characteristic measurement system based on the self-calibration probe spacing according to any one of the preceding embodiments, including:

s1: calibrating an initial spacing between each temperature sensing element in the temperature probe and the heating probe with a material having known thermal property parameters;

s2: inserting the temperature probe and the heating probe into a substance to be detected, measuring by a data acquisition processing device to obtain a curve of temperature changing along with time, calculating an in-situ actual distance between each temperature measuring element and the heating probe according to the curve of temperature changing along with time and the initial distance, and obtaining a thermal characteristic parameter of the substance to be detected by a single-point method or a nonlinear parameter fitting or regression method according to the in-situ actual distance.

The method for measuring the thermal characteristics of the two-pin thermal pulse capable of self-correcting the probe spacing in situ according to the embodiment of the invention can self-correct the probe spacing in situ, compared with the prior art that the probe is bent and cannot be corrected in situ or can be corrected, but based on the linear bending correction, the method can reduce the measurement error of the thermal characteristics parameters caused by the change of the probe spacing caused by the nonlinear bending deformation, thereby not only improving the accuracy of the two-pin thermal pulse method applied to measuring the thermal characteristics of the substance in the field, and the development of the double-needle heat pulse method is promoted, and in addition, the system has the advantages of simple structure, low manufacturing cost, convenience in use and quickness in measurement.

Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims (6)

1. A dual-probe heat pulse thermal characteristic measurement system capable of in-situ self-correcting probe spacing comprises a heating probe, a base, a heating device, a data processing device and at least one temperature probe,

temperature probe and heating probe are fixed along axial direction parallel on the base, set up the heater strip in the heating probe, the length of heating probe is greater than predetermined numerical value with the ratio of internal diameter, the heating probe is connected heating device utilizes heating device heats, is provided with at least three temperature element along its axial in every temperature probe, data processing device connects temperature element for obtain heating probe and temperature probe insert the material that awaits measuring after, the temperature data that temperature element gathered generates the temperature response curve, according to response curve utilizes normal position interval correction formula to calculate and obtains actual interval between temperature element and the heating probe, according to actual interval calculates the thermal property parameter who reachs the material that awaits measuring.

2. The system of claim 1, wherein if there is one temperature probe, the data processing device is configured to obtain a time period during which the temperature data collected by the temperature measurement element rises to a maximum value according to the curve, and calculate an actual distance between the temperature measurement element and the heating probe according to the time period, wherein the calculation formula is $r_i=a_1{l}_i+a_2{l}_i^2+......+a_{n-1}{l}_i^{n-1}+r_{i0},$

Wherein, a_iBy the formula

$\begin{array}{c}{\left(r_{10}+a_1{l}_1+......+a_{n-1}{l}_1^{n-1}\right)}^2{K}_1={\left(r_{20}+a_1{l}_2+......+a_{n-1}{l}_2^{n-1}\right)}^2{K}_2=\\ ......={\left(r_{n0}+a_1{l}_n+......+a_{n-1}{l}_n^{n-1}\right)}^2{K}_n\end{array}$

The calculation is carried out according to the calculation,r_iis the actual distance between the ith temperature measuring element and the heating probe,/_iIs the distance, r, from the ith temperature measuring element to the base_i0Is the initial spacing, t, between the ith temperature sensing element and the heater probe_miThe time length for which the temperature collected by the ith temperature measuring element rises to the maximum value, i ∈ (1,2, …, n), n is the number of temperature measuring elements in the temperature probe, t₀Is the heating time period of the heating probe.

3. The system of claim 1, wherein the data processing device is configured to derive the thermal property parameter of the substance to be measured by a single point method or a nonlinear parameter fitting and regression analysis method according to the actual distance.

4. The in-situ self-calibrating probe-spacing dual-probe heat pulse thermal property measurement system of claim 1, wherein said predetermined value is 22.

5. The self-correctable probe spacing dual pin heat pulse thermal profile measuring system of claim 1 wherein the distance between every two adjacent temperature sensing elements is greater than or equal to 2mm, the distance from the temperature sensing element near the tip of the temperature probe to the tip of the temperature probe is greater than or equal to 6mm, and the distance from the temperature sensing element near the base to the base is greater than or equal to 6 mm.

6. A measurement method of the dual-probe heat pulse thermal property measurement system based on the in-situ self-calibration probe spacing of any one of claims 1 to 5, comprising:

s1: calibrating an initial spacing between each temperature sensing element in the temperature probe and the heating probe with a material having known thermal property parameters;

s2: inserting the temperature probe and the heating probe into a substance to be detected, measuring by a data acquisition processing device to obtain a curve of temperature changing along with time, calculating an in-situ actual distance between each temperature measuring element and the heating probe according to the curve of temperature changing along with time and the initial distance, and obtaining a thermal characteristic parameter of the substance to be detected by a single-point method or a nonlinear parameter fitting or regression method according to the in-situ actual distance.